Development of a novel high-dimensional quantum squeezer
One of the project’s key outcomes is the theoretical design of a squeezer architecture tailored for high-dimensional quantum communication. Squeezed states are fundamental resources in quantum optics, enabling sensitivities beyond the shot-noise limit and supporting secure quantum information processing. Although experimental generation of such squeezed states in qudit or multidimensional protocols was not yet performed within QOMUNE, we developed a detailed theoretical model and performance analysis demonstrating that a compact, stable, and integrated squeezer can be made compatible with quantum photonic platforms. This work defines the required specifications and practical implementation pathways, establishing a clear roadmap toward future experimental realization and integration into multidimensional quantum networks.
Novel scheme for qudit interference via nonlinear optics
QOMUNE introduced a scalable theoretical framework for qudit interference that is independent of the specific degree of freedom employed. The proposed approach exploits nonlinear optical effects—both second- and third-order nonlinearities—to enable controlled interference between qudits of arbitrary dimensionality. This represents a significant step toward realizing complex, high-dimensional quantum operations in integrated photonic systems and provides a versatile foundation for future quantum communication and computation protocols.
Ultra-low-loss integrated photonic chip for quantum optics
A major achievement of the project is the design, fabrication, and experimental validation of an ultra-low-loss integrated photonic chip, developed in collaboration with an external foundry. The device implements a delay-line Mach–Zehnder interferometer, a fundamental component in many quantum photonics experiments. Integrated photonic platforms typically exhibit higher losses than fiber-based systems; our results overcame this limitation, achieving ultra-low optical loss, high interference visibility, and stable performance over extended measurement periods. This development demonstrates the feasibility of robust and scalable integrated photonic platforms for quantum communication experiments, including quantum key distribution (QKD).
Quantum key distribution over multicore fibers (MCF)
While most quantum communication experiments rely on standard single-mode fibers, the optical communications industry is transitioning toward high-bandwidth multicore fibers (MCF). QOMUNE successfully demonstrated QKD using qudits transmitted through deployed MCF infrastructure in the city of L’Aquila, Italy. The experiments confirmed the advantages of qudits over qubits in terms of key generation rate and resilience to losses. In addition, we studied the co-propagation of quantum and classical light in the same MCF, identifying optimal parameters for simultaneous transmission in the C-band. These findings pave the way for the practical integration of quantum and classical channels within next-generation optical networks.
